Re: [PATCH v3 4/4] drivers/thermal/exymos: Use guard notation when acquiring mutex

[Anand Moon <linux.amoon@gmail.com>]

Hi Lukasz,

On Wed, 5 Mar 2025 at 14:12, Lukasz Luba <lukasz.luba@arm.com> wrote:
>
>
>
> On 3/4/25 12:20, Anand Moon wrote:
> > Hi Lukasz,
> >
> > On Sat, 1 Mar 2025 at 00:06, Anand Moon <linux.amoon@gmail.com> wrote:
> >>
> >> Hi Lukasz,
> >>
> >> On Fri, 28 Feb 2025 at 22:58, Lukasz Luba <lukasz.luba@arm.com> wrote:
> >>>
> >>>
> >>>
> >>> On 2/16/25 19:58, Anand Moon wrote:
> >>>> Using guard notation makes the code more compact and error handling
> >>>> more robust by ensuring that mutexes are released in all code paths
> >>>> when control leaves critical section.
> >>>>
> >>>> Signed-off-by: Anand Moon <linux.amoon@gmail.com>
> >>>> ---
> >>>> v3: new patch
> >>>> ---
> >>>>    drivers/thermal/samsung/exynos_tmu.c | 21 +++++++--------------
> >>>>    1 file changed, 7 insertions(+), 14 deletions(-)
> >>>>
> >>>> diff --git a/drivers/thermal/samsung/exynos_tmu.c b/drivers/thermal/samsung/exynos_tmu.c
> >>>> index fe090c1a93ab..a34ba3858d64 100644
> >>>> --- a/drivers/thermal/samsung/exynos_tmu.c
> >>>> +++ b/drivers/thermal/samsung/exynos_tmu.c
> >>>> @@ -256,7 +256,7 @@ static int exynos_tmu_initialize(struct platform_device *pdev)
> >>>>        unsigned int status;
> >>>>        int ret = 0;
> >>>>
> >>>> -     mutex_lock(&data->lock);
> >>>> +     guard(mutex)(&data->lock);
> >>>>        clk_enable(data->clk);
> >>>>        clk_enable(data->clk_sec);
> >>>>
> >>>> @@ -270,7 +270,6 @@ static int exynos_tmu_initialize(struct platform_device *pdev)
> >>>>
> >>>>        clk_disable(data->clk_sec);
> >>>>        clk_disable(data->clk);
> >>>> -     mutex_unlock(&data->lock);
> >>>>
> >>>>        return ret;
> >>>>    }
> >>>> @@ -292,13 +291,12 @@ static int exynos_thermal_zone_configure(struct platform_device *pdev)
> >>>>                return ret;
> >>>>        }
> >>>>
> >>>> -     mutex_lock(&data->lock);
> >>>> +     guard(mutex)(&data->lock);
> >>>>        clk_enable(data->clk);
> >>>>
> >>>>        data->tmu_set_crit_temp(data, temp / MCELSIUS);
> >>>>
> >>>>        clk_disable(data->clk);
> >>>> -     mutex_unlock(&data->lock);
> >>>>
> >>>>        return 0;
> >>>>    }
> >>>> @@ -325,12 +323,11 @@ static void exynos_tmu_control(struct platform_device *pdev, bool on)
> >>>>    {
> >>>>        struct exynos_tmu_data *data = platform_get_drvdata(pdev);
> >>>>
> >>>> -     mutex_lock(&data->lock);
> >>>> +     guard(mutex)(&data->lock);
> >>>>        clk_enable(data->clk);
> >>>>        data->tmu_control(pdev, on);
> >>>>        data->enabled = on;
> >>>>        clk_disable(data->clk);
> >>>> -     mutex_unlock(&data->lock);
> >>>>    }
> >>>>
> >>>>    static void exynos_tmu_update_bit(struct exynos_tmu_data *data, int reg_off,
> >>>> @@ -645,7 +642,7 @@ static int exynos_get_temp(struct thermal_zone_device *tz, int *temp)
> >>>>                 */
> >>>>                return -EAGAIN;
> >>>>
> >>>> -     mutex_lock(&data->lock);
> >>>> +     guard(mutex)(&data->lock);
> >>>>        clk_enable(data->clk);
> >>>>
> >>>>        value = data->tmu_read(data);
> >>>> @@ -655,7 +652,6 @@ static int exynos_get_temp(struct thermal_zone_device *tz, int *temp)
> >>>>                *temp = code_to_temp(data, value) * MCELSIUS;
> >>>>
> >>>>        clk_disable(data->clk);
> >>>> -     mutex_unlock(&data->lock);
> >>>>
> >>>>        return ret;
> >>>>    }
> >>>> @@ -720,11 +716,10 @@ static int exynos_tmu_set_emulation(struct thermal_zone_device *tz, int temp)
> >>>>        if (temp && temp < MCELSIUS)
> >>>>                goto out;
> >>>>
> >>>> -     mutex_lock(&data->lock);
> >>>> +     guard(mutex)(&data->lock);
> >>>>        clk_enable(data->clk);
> >>>>        data->tmu_set_emulation(data, temp);
> >>>>        clk_disable(data->clk);
> >>>> -     mutex_unlock(&data->lock);
> >>>>        return 0;
> >>>>    out:
> >>>>        return ret;
> >>>> @@ -760,14 +755,13 @@ static irqreturn_t exynos_tmu_threaded_irq(int irq, void *id)
> >>>>
> >>>>        thermal_zone_device_update(data->tzd, THERMAL_EVENT_UNSPECIFIED);
> >>>>
> >>>> -     mutex_lock(&data->lock);
> >>>> +     guard(mutex)(&data->lock);
> >>>>        clk_enable(data->clk);
> >>>>
> >>>>        /* TODO: take action based on particular interrupt */
> >>>>        data->tmu_clear_irqs(data);
> >>>>
> >>>>        clk_disable(data->clk);
> >>>> -     mutex_unlock(&data->lock);
> >>>>
> >>>>        return IRQ_HANDLED;
> >>>>    }
> >>>> @@ -987,7 +981,7 @@ static int exynos_set_trips(struct thermal_zone_device *tz, int low, int high)
> >>>>    {
> >>>>        struct exynos_tmu_data *data = thermal_zone_device_priv(tz);
> >>>>
> >>>> -     mutex_lock(&data->lock);
> >>>> +     guard(mutex)(&data->lock);
> >>>>        clk_enable(data->clk);
> >>>>
> >>>>        if (low > INT_MIN)
> >>>> @@ -1000,7 +994,6 @@ static int exynos_set_trips(struct thermal_zone_device *tz, int low, int high)
> >>>>                data->tmu_disable_high(data);
> >>>>
> >>>>        clk_disable(data->clk);
> >>>> -     mutex_unlock(&data->lock);
> >>>>
> >>>>        return 0;
> >>>>    }
> >>
> >> Thanks for your review comments.
> >>>
> >>> IMO you should be able to even use something like we have
> >>> core framework:
> >>>
> >>> guard(thermal_zone)(tz);
> >>>
> >>> Your mutex name is simply 'lock' in the struct exynos_tmu_data
> >>> so you should be able to leverage this by:
> >>>
> >>> guard(exynos_tmu_data)(data);
> >>>
> >
> > If I introduce the guard it creates a compilation error
> >
> > amoon@anand-m920q:~/mainline/linux-exynos-6.y-devel$ vi
> > drivers/thermal/samsung/exynos_tmu.c +306
> > amoon@anand-m920q:~/mainline/linux-exynos-6.y-devel$ make -j$(nproc)
> > ARCH=arm CROSS_COMPILE=arm-none-eabi- LOCALVERSION=-u3ml dtbs zImage
> > modules
> >    CALL    scripts/checksyscalls.sh
> >    CHK     kernel/kheaders_data.tar.xz
> >    CC      drivers/thermal/samsung/exynos_tmu.o
> >    CC [M]  drivers/md/raid10.o
> > In file included from ./include/linux/irqflags.h:17,
> >                   from ./arch/arm/include/asm/bitops.h:28,
> >                   from ./include/linux/bitops.h:68,
> >                   from ./include/linux/kernel.h:23,
> >                   from ./include/linux/clk.h:13,
> >                   from drivers/thermal/samsung/exynos_tmu.c:14:
> > drivers/thermal/samsung/exynos_tmu.c: In function 'exynos_tmu_update_bit':
> > ./include/linux/cleanup.h:258:9: error: unknown type name
> > 'class_exynos_tmu_data_t'
> >    258 |         class_##_name##_t var
> > __cleanup(class_##_name##_destructor) =   \
> >        |         ^~~~~~
> > ./include/linux/cleanup.h:309:9: note: in expansion of macro 'CLASS'
> >    309 |         CLASS(_name, __UNIQUE_ID(guard))
> >        |         ^~~~~
> > drivers/thermal/samsung/exynos_tmu.c:338:9: note: in expansion of macro 'guard'
> >    338 |         guard(exynos_tmu_data)(data);
> >        |         ^~~~~
> > drivers/thermal/samsung/exynos_tmu.c:338:9: error: cleanup argument
> > not a function
>
> [snip]
>
> Right, you're missing the definition at the begging, like:
>
> DEFINE_GUARD(exynos_tmu_data, struct exynos_tmu_data *,
> mutex_lock(&_T->lock),
>               mutex_unlock(&_T->lock))
>
> below the struct exynos_tmu_data definition.
>
> Also, make sure you include the cleanup.h (it might not complain,
> but it would be explicit and more clear)

Thanks for this tip.
However, incorporating guard(exynos_tmu_data)(data); results
in a recursive deadlock with the mutex during initialization, as this
data structure is common to all the code configurations of Exynos TMU

Thanks
-Anand